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Large‐scale production of two‐dimensional (2D) materials still is a crucial point toward its practical applications. Violet phosphorus (VP) with a wide bandgap accelerates and broadens the potential applications of elemental phosphorus in optoelectronics. Here, we demonstrate the scalable production of solution‐processable violet phosphorus flakes stably dispersed in several solvents. The exfoliated VP flakes exhibit thickness‐dependent visible photoluminescence characteristics, which covers the shortcoming of black phosphorus. Meanwhile, the VP‐based field‐effect transistor reveals relatively competitive electrical properties to other liquid‐phase exfoliated 2D materials. Our study paves the way for a wide range of applications of optical devices, energy storage, catalysis, and sodium batteries based on large‐scale VP flakes.

Group‐10 transition metal dichalcogenides (TMDs) with distinct optical and tunable electrical properties have exhibited great potential for various optoelectronic applications. Herein, a self‐powered photodetector is developed with broadband response ranging from deep ultraviolet to near‐infrared by combining FA1−xCsxPbI3 perovskite with PdSe2 layer, a newly discovered TMDs material. Optoelectronic characterization reveals that the as‐assembled PdSe2/perovskite Schottky junction is sensitive to light illumination ranging from 200 to 1550 nm, with the highest sensitivity centered at ≈800 nm. The device also shows a large on/off ratio of ≈104, a high responsivity (R) of 313 mA W−1, a decent specific detectivity (D*) of ≈1013 Jones, and a rapid response speed of 3.5/4 µs. These figures of merit are comparable with or much better than most of the previously reported perovskite detectors. In addition, the PdSe2/perovskite device exhibits obvious sensitivity to polarized light, with a polarization sensitivity of 6.04. Finally, the PdSe2/perovskite detector can readily record five “P,” “O,” “L,” “Y,” and “U” images sequentially produced by 808 nm. These results suggest that the present PdSe2/perovskite Schottky junction photodetectors may be useful for assembly of optoelectronic system applications in near future.

A vertical graphene heterostructure field-effect transistor (VGHFET) using an ultrathin ferroelectric film as a tunnel barrier is developed. The heterostructure is capable of providing new degrees of tunability and functionality via coupling between the ferroelectricity and the tunnel current of the VGHFET, which results in a high-performance device. The results pave the way for developing novel atomic-scale 2D heterostructures and devices.

We report a new mechanistic strategy for controlling and modifying the photon emission of lanthanides in a core-shell nanostructure by using interfacial energy transfer. By taking advantage of this mechanism with Gd(3+) as the energy donor, we have realized efficient up- and down-converted emissions from a series of lanthanide emitters (Eu(3+) , Tb(3+) , Dy(3+) , and Sm(3+) ) in these core-shell nanoparticles, which do not need a migratory host sublattice. Moreover, we have demonstrated that the Gd(3+) -mediated interfacial energy transfer, in contrast to energy migration, is the leading process contributing to the photon emission of lanthanide dopants for the NaGdF4 @NaGdF4 core-shell system. Our finding suggests a new direction for research into better control of energy transfer at the nanometer length scale, which would help to stimulate new concepts for designing and improving photon emission of the lanthanide-based luminescent materials.

Black phosphorus (BP) is a very promising material for telecommunication due to its direct bandgap and strong resonant absorption in near-infrared wavelength range. However, ultrafast nonlinear photonic applications relying on the ultrafast photocarrier dynamics as well as optical nonlinearity in black phosphorus remain unexplored. In this work, nonlinear optical properties of solution exfoliated BP are investigated and the usage of BP as a new saturable absorber for high energy pulse generation in fiber laser is demonstrated. In order to avoid the oxidization and degradation, BP is encapsulated by polymer matrix which is optically transparent in the spectrum range of interest to form a composite. Two fabrication approaches are demonstrated to produce BP-polymer composite films which are further incorporated into fiber laser cavity as nonlinear media. BP shows very fast carrier dynamics and BP-polymer composite has a modulation depth of 10.6%. A highly stable Q-switched pulse generation is achieved and the single pulse energy of 194 nJ is demonstrated. The ease of handling of such black phosphorus-polymer composite thin films affords new opportunities for wider applications such as optical sensing, signal processing, and light modulation.

Amorphous black phosphorus (a-BP) ultrathin films are deposited by pulsed laser deposition. a-BP field-effect trans-istors, exhibiting high carrier mobility and moderate on/off current ratio, are demonstrated. Thickness dependence of the bandgap, mobility, and on/off ratio are observed. These results offer not only a new nanoscale member in the BP family, but also a new opportunity to develop nano-electronic devices.

We report a simple approach based on a chemical reduction method to synthesize aqueous inorganic ink com- prised of hexagonal MnO2 nanosheets. The MnO2 ink exhibits long-term stability and continuous thin films can be formed on various substrates without using any binder. To obtain a flexible electrode for capacitive energy storage, the MnO2 ink was printed onto commercially available A4 paper pretreated with multiwalled carbon nanotubes. The electrode exhibited a max- imum specific capacitance of 1035 F g � 1 (91.7 mF cm � 2 ). Paper- based symmetric and asymmetric capacitors were assembled, which gave a maximum specific energy density of 25.3 Wh kg � 1 and a power density of 81 kW kg � 1 . The device could maintain a 98.9 % capacitance retention over 10 000 cycles at 4 A g � 1 . The MnO2 ink could be a versatile candidate for large-scale production of flexible and printable electronic devices for energy storage and conversion.

Gallium selenide, an important second-order nonlinear semiconductor, has received much scientific interest. However, the nonlinear properties in its two-dimensional (2D) form are still unknown. A strong second harmonic generation (SHG) in bilayer and multilayer GaSe sheets is reported. This is also the first observation of SHG on 2D GaSe thin layers. The SHG of multilayer GaSe above five layers shows a quadratic dependence on the thickness; while that of a sheet thinner than five layers shows a cubic dependence. The discrepancy between the two SHG responses is attributed to the weakened stability of non-centrosymmetric GaSe in the atomically thin flakes where a layer-layer stacking order tends to favor centrosymmetric modification. Importantly, two-photon excited fluorescence has also been observed in the GaSe sheets. Our free-energy calculations based on first-principles methods support the observed nonlinear optical phenomena of the atomically thin layers.

Ferroelectric domain walls exhibit a number of new functionalities that are not present in their host material. One of these functional characteristics is electrical conductivity that may lead to future device applications. Although progress has been made, the intrinsic conductivity of BiFeO3 domain walls is still elusive. Here, the intrinsic conductivity of 71° and 109° domain walls is reported by probing the local conductance over a cross section of the BiFeO3 /TbScO3 (001) heterostructure. Through a combination of conductive atomic force microscopy, high-resolution electron energy loss spectroscopy, and phase-field simulations, it is found that the 71° domain wall has an inherently charged nature, while the 109° domain wall is close to neutral. Hence, the intrinsic conductivity of the 71° domain walls is an order of magnitude larger than that of the 109° domain walls associated with bound-charge-induced bandgap lowering. Furthermore, the interaction of adjacent 71° domain walls and domain wall curvature leads to a variation of the charge distribution inside the walls, and causes a discontinuity of potential in the [110]p direction, which results in an alternative conductivity of the neighboring 71° domain walls, and a low conductivity of the 71° domain walls when measurement is taken from the film top surface.

12 ] Therefore, graphene-based IR detectors have much lower responsivities than photoconductors based on QDs. It is reasonable to consider that the responsivity of a graphene-based IR detector can be improved substantially by modifying the graphene fi lm with QDs, which can absorb IR light more effi ciently. On the other hand, if the carriers gener-ated by IR light can transfer to the graphene fi lm, their mobility will be much higher and thus the responsivity will be dramati-cally improved for a QD-based IR detector. Moreover, an array of graphene devices can be easily patterned by state-of-the-art techniques and this could possibly lead to elimination of the crosstalk between neighboring pixels that occur in silicon devices.

This work shows the large‐area growth of high‐quality vertically aligned PtSe 2 , and its application to photodetectors based on PtSe 2 ‐GaAs heterojunctions which exhibit a broadband sensitivity to illumination ranging from deep ultraviolet to near‐infrared light, with a peak sensitivity in the region from 650 to 810 nm. The high‐performance broadband photodetector will develop the next‐generation 2D Group‐10 materials based optoelectronic devices.

Wurtzite structure ZnO films doped with 0.5 and 1.7 at% Cu were deposited by helicon magnetron sputtering. The prepared films exhibited room-temperature (RT) ferromagnetism (FM). Maximum RT saturation magnetization of 2 emu/cm3 (∼0.3μB/Cu) was observed for ZnO film with 1.7 at% Cu. Cu ions were in a bivalent state as identified by X-ray photoelectron spectroscopy (XPS). In photoluminescence spectra, the green emission peak increased and redshifted due to the incorporation of Cu or defects induced by Cu incorporation. Since Cu and Cu-related oxides are not RT ferromagnetic, and no trace of ferromagnetic contamination was detected in XPS results, the observed FM is considered to be an intrinsic property of Cu-doped ZnO films. The FM was thought to originate from defect-related mechanisms. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple catalysis-free approach that utilises a gas-solid reaction for the synthesis of large-scale single-crystalline PrB 6 nanorods using Pr and BCl 3 as starting materials is demonstrated. The nanorods exhibit a low turn-on electric field (2.80V μm -1 at 10 μA cm -2 ), a low threshold electric field (6.99V μm -1 at 1 mA cm -2 ), and a high current density (1.2 mA cm -2 at 7.35 V μm -1 ) at room temperature (RT). The turn-on and threshold electric field are found to decrease clearly from 2.80 to 0.95 and 6.99 to 3.55 V μm -1 , respectively, while the emission current density increases significantly from 1.2 to 13.8 mA cm -2 (at 7.35V μm -1 ) with an increase in the ambient temperature from RT to 623 K. The field enhancement factor, emission current density, and the dependence of the effective work function with temperature are investigated. The possible mechanism of the temperature-dependent emission from PrB 6 nanorods is discussed.

Vertically self-aligned conical carbon nanofibers were deposited on silicon coated with thin film of cobalt (100 nm) using pulsed discharge plasma chemical vapor deposition at 400–450 °C. Possible mechanism of their growth is discussed. FE-SEM observations indicate that they are self vertically well aligned, with an average diameter of about 200 nm at the bottom and with a tip of about 70 to 100 nm in diameter. HR-TEM, visible Raman and XRD study reveals that the nanofibers have an amorphous structure and are made of diamond like carbon. Field electron emission study indicates a low turn-on field of about 1.4 V/μm and threshold field of about 4.2 V/μm, suggesting their possible application as field electron emitters. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This work was supported by NTU RGM 17/04, the National Creative Research Initiative Project, and the Center for Nanostructured Materials Technology under the 21st Century Frontier R&D Program of the Ministry of Science and Technology, Korea.

The electrical and optical measurements, in combination with density functional theory calculations, show distinct layer-dependent semiconductor-to-semimetal evolution of 2D layered PtSe2 . The high room-temperature electron mobility and near-infrared photo-response, together with much better air-stability, make PtSe2 a versatile electronic 2D layered material.

The giant anisotropic Raman response of encapsulated ultrathin black phosphorus (BP) is reported by uniaxial strain. A modified bending technique is employed to apply precise uniaxial tensile strain along the zigzag or armchair direction of the ultrathin BP encapsulated by a layer of polymethyl methacrylate. The Raman shift rates of the A 1 g, B 2g, and A 2 g modes are significantly distinct for strain applied along different directions. For the strain applied along zigzag direction, the Raman shift rate of the B 2g mode can reach a remarkable value of ≈−11 cm−1/% strain. In addition, the Gruneisen parameter is as high as ≈2.5, which is the largest among all the reported common 2D materials. Density functional perturbation theory calculations are performed to understand the exceptional anisotropic strain response discovering that not only the bond lengths but also the bond angels are changed in the strained ultrathin BP, which lead to the giant anisotropic Raman response. Furthermore, an alternative method based entirely on the strained ultrathin BP and nonpolarized Raman spectroscopy is demonstrated to determine the crystallographic orientations of ultrathin BP. This work paves a way to study the strain-induced anisotropic electrical conductance and magnetotransport properties of BP.

This review paper summarises briefly some important achievements of our recent research on the synthesis and novel applications of nanostructure ZnO such as honeycomb shaped 3-D (dimension) nano random-walls. A chemical reaction/vapour transportation deposition technique was employed to fabricate this structure on ZnO/SiO2/Si substrate without any catalyst and additive in a simple tube furnace to aim the low-cost and high qualified samples. Random laser action with strong coherent feedback at the wavelength between 375 nm and 395 nm has been firstly observed under 355 nm optical excitation with threshold pumping intensity of 0.38 MW/cm(2).

Room-temperature ultraviolet random lasing with low threshold pumping power was successfully achieved by ZnO 3-D random-wall nanostructure fabricated on ZnO/SiO2/Si substrate through a thermal chemical reaction and vapor transportation deposition method in a simple horizontal tube furnace from the mixed ZnO and graphite powders. The nanorods grown along c-axis on the substrate are coalesced to form the 3-D nano-wall with 80∼100 nm in wall thickness and irregular height ranging of 95-250 nm. Mueller matrix spectroscopic ellipsometry reveals that evaluated refractive indices n (E) of ZnO nanowalls are well interpreted by taking account of the ratio between ZnO and void achieved by effective medium theory analysis and isotropic depolarization feature of the designated nanowalls. Random lasing action observed in the wide wavelength range between 375 and 395 nm is realized by coherent amplification of the closed-loop scattered light inside 3-D random-wall nanostructure. It is demonstrated that both transverse electric (TE) and transverse magnetic (TM) modes show the same threshold and pumping power dependent trend, while the intensity of TM lasing is weaker than that of TE due to the different scattering strength originated from the features of the inside of nano wall. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)